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My XML sitemap file has <lastmod>2013-07-06T09:39:51-0400</lastmod> formatted with W3C Datetime Format. Google has a warning message in webmaster tools about this for me:

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Google's help document about error sitemap errors states:

This could be because a date is in the incorrect format, or the date itself is not valid. Dates must use W3C Datetime encoding, although you can omit the time portion if you wish. For example:

  • 2005-02-21
  • 2005-02-21T18:00:15+00:00
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up vote 2 down vote accepted


The W3C datetime format includes a : (colon) in the time zone offset, separating the hours and minutes. So the last bit should read: -04:00.

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